1. Field of the Invention
The present invention relates to an enclosed motor-driven compressor for use in a refrigerator or the like.
2. Description of the Prior Art
In recent years, there has been an increased demand for a highly efficient enclosed motor-driven compressor (hereinafter referred to as "compressor") from the viewpoint of increasing the energy efficiency. The efficiency of the compressors has been increased to a certain high level, however, a further improvement is needed.
Japanese Patent Laid-open Publication No. 63-5186 exemplifies one conventional compressor which includes, as shown here in FIG. 5, a closed container 1 within which a motor element 2 and a compressor element 3 are resiliently supported. The motor element 2 is composed of a stator 4 and a rotor 5. The rotor 5 has a central hole in which a crankshaft 6 is firmly fitted. The crankshaft 6 is rotatably supported by a pair of ball bearings 7 and 8 mounted in a housing 9. The ball bearings 7 and 8 are press-fitted over the crankshaft 6 and retained at predetermined positions, respectively, within a stepped bore in the housing 9. The housing 9 is secured to a cylinder block 10 by a plurality of screws 11 (only one shown). A lubricating oil 12 is held at the bottom of the container 1. Though not shown, the crankshaft 6 has an axial groove connected at one end (inlet) to an oil feed pipe 13 immersed in the lubricating oil 12, the opposite end (outlet) of the axial groove opening at a portion of the crankshaft 6 which is disposed above the ball bearing 7 for a purpose described below. The crankshaft 6 is connected by a connecting rod 14 to a piston 15 slidably received in a cylinder bore 16 in the cylinder block 10.
In operation, when the motor element 2 is energized to start operation of the compressor of the foregoing construction, the rotor 5 and the crankshaft 6 rotate. Since the crankshaft 6 is connected to the piston 15 by the connecting rod 14, a rotary motion of the crankshaft 6 is changed into a reciprocating motion of the piston 15 which in turn compresses a refrigerating agent trapped in the gaseous state within a compression chamber defined between the cylinder block 10 and the piston 15. The lubricating oil 12 is sucked by a centrifugal force from the oil feed pipe 13, then flows upward along the axial groove in the crankshaft 6, and finally supplied from the outlet of the axial groove onto the ball bearing 7 and thence to the ball bearing 8.
Since the crankshaft 6 of the conventional compressor is supported only at one side with respect to a point of application of a reaction force of the compression load of the piston 15 (i.e., the crankshaft 6 has a cantilevered or overhanging structure), the reaction force W of the compression load acts on the ball bearings 7 and 8 in the manner diagrammatically shown in FIG. 6. As is apparent from FIG. 6, a load exerted on the ball bearing 8 is represented by L/l.sub.2 .multidot.W where L is the distance between the point of application of the reaction force W and the ball bearing 7, l.sub.2 is the distance between the ball bearing 7 and the ball bearing 8, and W is the reaction force of the compression load of the piston 15. Likewise, a load acting on the ball bearing 7 is represented by l.sub.1 /l.sub.2 .multidot.W where l is the distance between the ball bearing 8 and the point of application of the reaction force W, l.sub.2 is as defined above, and W is as defined above. This means that the load acting on the ball bearing 8 exceeds the reaction force W. On the other hand, the load on the ball bearing 7 is smaller than the reaction force W but it still has a relatively large magnitude. With this distribution of bearing loads, the ball bearings 7 and 8 have a relatively short service life and hence are difficult to provide a sufficient degree of reliability. in addition, since the direction of the load acting on the ball bearing 7 is opposite to the direction of the load on the ball bearing 8, and due to the presence of internal radial clearances of the respective ball bearings 7 and 8, the rotor 5 while it is rotating tends to vibrate in a precessional manner. With this precessional vibration, a gap between the stator 4 and rotor 5 cannot be maintained uniformly, so that the motor efficiency tends to fluctuate.
In addition, since it takes about several seconds before the lubricating oil 12 reaches the ball bearings 7 and 8, the ball bearings 7 and 8 may be marked with scars or dents before they are lubricated. the ball bearings 7 and 8 thus damaged have a short service life and cannot operate stably and reliably.
Japanese Patent Laid-open Publication No. 63-134872 discloses another conventional compressor which comprises, as shown in FIG. 7, a corrugated spring washer 16 disposed, in a somewhat distorted state, between an outer race 8a of the ball bearing 8 and the housing 9, and a sleeve 17 fitted over the crankshaft 6 and held in contact with an inner race of the ball bearing 7 to lock the crankshaft 6 in position against axial displacement relative to the ball bearings 7 and 8. These parts which correspond to those of the conventional compressor shown in FIG. 5 are designated by the same or corresponding characters, and a further description thereof will be omitted.
With the construction, the ball bearing 7 is subjected to a thrust load exerted by the spring washer 16 in addition to the weight of the rotor 5 and the crankshaft 6, while the ball bearing 8 is subjected to the thrust load from the spring washer 16. The spring washer 16 serves to lighten the influence of the weight of the rotor 5 and the crankshaft 6 on the ball bearings 7 and 8 so as to lower the sliding noise of the ball bearings 7 and 8. The last-mentioned conventional compressor also has the low motor efficiency problem and the insufficient lubrication problem that are mentioned above with respect to the compressor disclosed in the first-mentioned Japanese publication.